A Self-Flux-Biased NanoSQUID with Four NbN-TiN-NbN Nanobridge Josephson Junctions

Round 1

Reviewer 1 Report

We have developed planar 4-Josephson-junction nanoscale superconducting quantum interference devices (nanoSQUIDs), which are self-biased to optimal sensitivity without application of magnetic flux of Φ0/4. In the nanoSQUIDs we invented novel NbN-TiN-NbN nanobridge Josephson junctions (nJJs) that contain NbN current leads and the electrodes of the nanoSQUID body connected by the TiN nanobridges. TiN exhibits combination of an optimal superconducting transition temperature ∼4.8 K, superconducting coherence length ∼100 nm and corrosion resistance for hysteresis-free, reproducible and long-term stability for nJJ and nanoSQUID operation at 4.2 K, while corrosion-resistant NbN provides relatively high superconducting transition temperatures ∼15 K and correspondingly large energy gap. FIB patterning of TiN films and nanoscale sculpturing of tip area of nanoSQUID’s cantilevers were performed using amorphous Al films as sacrificial layers due to their relatively high chemical reactivity to alkalis. Cantilever with distance between nanoSQUID and substrate corner ∼300 nm was realized. The I(V)-characteristics of the nJJs and nanoSQUIDs as well as the voltage modulation of the nanoSQUIDs were measured at 4.2 K. The developed technology can be used for fabrication of durable nanoSQUID sensors for low-temperature magnetic microscopy as well as for realization of more complex circuits of superconducting nanobridge electronics. Generally, this is a good work. It can be accepted if the authors can consider the following issues:1. The motivations of the work should be well organized. 2. The original contribution of the work should be added in the introduction part. 3. More related works on the optimization are welcome to enrich the literature review such as Fault diagnosis of an autonomous vehicle with an improved SVM algorithm subject to unbalanced datasets;Tuning of digital PID controllers using particle swarm optimization algorithm for a CAN-based DC motor subject to stochastic delays 4. The quality of Figure 1 should be improved. Why one in color and one in white-black? 5. The writing should be improved as well.

Author Response

We are very grateful to the referee for taking the time to read our paper and for the helpful and constructive comments. Point-by-point replies to the reviewers’ comments are included below. The corresponding changes in the revised manuscript are highlighted in color.

>1. The motivations of the work should be well organized.

We have amended the introduction in this direction. We have added two sentences at the beginning and made additional changes in the text.

>2. The original contribution of the work should be added in the introduction part.

Done: References 7, 12, 22 and 27 are our contributions to the work cited in the introduction part.

>3. More related works on the optimization are welcome to enrich the literature review such as Fault diagnosis of an autonomous vehicle with an improved SVM algorithm subject to unbalanced datasets; Tuning of digital PID controllers using particle swarm optimization algorithm for a CAN-based DC motor subject to stochastic delays

Done: The introduction describes the history of the optimization of the technology of Josephson junctions and nanoSQUIDs.

>4. The quality of Figure 1 should be improved. Why one in color and one in white-black?

Done: Now both images are in grayscale.

>5. The writing should be improved as well.

Done: The manuscript has been checked by a native English speaker. Furthermore, we have made some additional minor changes due to error correction and rewriting since the first submission.

Reviewer 2 Report

Very important technique discovered using NbN-TiN-NbN nJJs and planar 4-JJ nanoSQUIDs using pattering methods. In future the technology should lead to the fabrication of durable nanoSQUID sensors for low-temperature magnetic microscopy and in-situ microscopy. 

Author Response

The request to improve the language has been realised. The manuscript has been checked by a native English speaker. Furthermore, we have made some additional minor changes due to error correction and rewriting since the first submission. The corresponding changes in the revised manuscript are highlighted in color.